%0 Journal Article
%T Ortho-Para Selection Rules in the Gas-phase Chemistry of Interstellar Ammonia
%+ Institut de Planétologie et d'Astrophysique de Grenoble (IPAG )
%+ Institut d'astrophysique spatiale (IAS)
%A Faure, A.
%A Hily-Blant, P.
%A Le Gal, R.
%A Rist, C.
%A Pineau Des Forêts, G.
%< avec comité de lecture
%J The Astrophysical Journal Letters
%V 770
%8 2013
%D 2013
%Z 2013ApJ...770L...2F
%R 10.1088/2041-8205/770/1/L2
%K astrochemistry
%K ISM: molecules
%K molecular processes
%Z Sciences of the Universe [physics]Journal articles
%X The ortho-para chemistry of ammonia in the cold interstellar medium is investigated using a gas-phase chemical network. Branching ratios for the primary reaction chain involved in the formation and destruction of ortho- and para-NH3 were derived using angular momentum rules based on the conservation of the nuclear spin. We show that the "anomalous" ortho-to-para ratio of ammonia (~0.7) observed in various interstellar regions is in fact consistent with nuclear spin selection rules in a para-enriched H2 gas. This ratio is found to be independent of temperature in the range 5-30 K. We also predict an ortho-to-para ratio of ~2.3 for NH2. We conclude that a low ortho-to-para ratio of H2 naturally drives the ortho-to-para ratios of nitrogen hydrides below the statistical values.
%G English
%L insu-03617070
%U https://insu.hal.science/insu-03617070
%~ INSU
%~ UNIV-SAVOIE
%~ UGA
%~ CNRS
%~ UNIV-GRENOBLE1
%~ UNIV-PSUD
%~ INPG
%~ IRSTEA
%~ CNES
%~ OSUG
%~ IPAG
%~ UNIV-PARIS-SACLAY
%~ AGREENIUM
%~ UNIV-PSUD-SACLAY
%~ INRAE
%~ USMB-COMUE
%~ GS-PHYSIQUE
%~ IAS